This application is based upon, claims the benefit of priority of, and incorporates by reference the contents of prior Japanese Application No. 2001-318334 filed Oct. 16, 2001.
1. Technical Field of the Invention
The present invention relates to an engine starter including a current control unit for controlling the current flowing in an exciting coil of an electromagnetic switch and the current flowing in a starter motor.
2. Description of Related Art
In general, when an ignition switch is turned on, an electromagnetic switch provided in a starter generates magnetic force by energizing its exciting coil, and pushes a pinion out by driving a plunger that uses the magnetic force. At this time, when the moving speed of the plunger is high, the pinion contacts a ring gear with a large impact, and its collision sound is heightened. Further, the ring gear becomes worn by repeating this contact.
In related prior art for solving the problems, current flowing into the exciting coil is restricted through a control device connected in series to the exciting coil, thereby reducing the moving speed of the plunger. Further, the main current, that is, the current flowing into the starter motor, is controlled to control characteristics of the starter motor. However, since the main current for the starter motor is much larger than the current flowing into the exciting coil, it is extremely difficult to control the main current using the control device for controlling the current of the exciting coil. Therefore, a control device, different from the control device for controlling the current of the exciting coil, needs to be newly created and provided to control the main current. Further, both control devices need to be controlled by different control circuits, respectively.
As described above, if not only the current control for the exciting coil, but also the main-current control for the starter motor are performed, a control system is complicated, and production costs are largely increased.
The present invention has been made in view of the above problems, and it is an object of the present invention to provide an engine starter with a control system that can be simplified by integrating current control for an exciting coil and integrating main current control for a starter motor.
An engine starter according to a first aspect of the present invention includes a control device provided among a battery, a motor contact point and an exciting coil, and a current control unit for controlling current (coil current) flowing into the exciting coil and current (main current) flowing into a starter motor using the control device. The current control unit changes a control specification for the control device between before and after closing the motor contact point.
Since the present invention uses a control device capable of allowing the main current, a common current control unit can control the coil current and the main current. As a result, a control system can be simplified compared to a case where the coil current and the main current are controlled by separated control devices, respectively.
In the engine starter according to a second aspect of the invention, the current control unit restricts current flowing into the exciting coil to a predetermined value using the control device to reduce the moving speed of the plunger after starting energization of the exciting coil. As soon as the contact-point detecting device detects the closed state of the motor contact point, current control is released for the exciting coil, and a current flowing into the starter motor is gradually increased using the control device to restrict a rush current flowing into the starter motor.
According to this construction, since the moving speed of the plunger is reduced by restricting the coil current to the predetermined value, the moving speed of the pushed pinion can be reduced while interlocked with movement of the plunger. As a result, impact force, generated when the pinion contacts a ring gear, is reduced, thereby reducing impact noise, and restricting wear of the gear, edges of the gear and the like.
Further, when the moving speed of the plunger is reduced, bounce of a movable contact point, provided on the plunger, is reduced. This restricts an arc current due to the bounce, and prevents the motor contact point and the movable contact point from melting and adhering to each other. After closing the motor contact point, since a rush current can be prevented by slowly raising the main current, the brush can be prevented from premature wear.
In the engine starter according to the above second aspect, the current control unit performs pulse width modulation control (PWM control) for a voltage output from a battery by turning the control device on and off. Furthermore, the current control unit switches any one of a current control for the exciting coil and a current control for the starter motor by changing a specification of the PWM control. Accordingly, according to a third aspect of the invention, the coil current and the main current can be controlled by controlling a voltage between terminals of the exciting coil and a voltage between terminals of the starter motor, respectively.
In the engine starter according to the above second and third aspects, the current control unit determines current-control start timing using a battery voltage. When the plunger is driven, the entire voltage is applied to the exciting coil at first. However, when the battery voltage is high, a transient build-up speed of the plunger becomes high. Therefore, the time that the voltage is applied is changed in accordance with the battery voltage, thereby suitably controlling the moving speed of the plunger.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.